This invention relates to composite sandwich structures, and particularly concerns the production of contoured sandwich radomes.
Enclosures for radiant electrical energy transmitting and receiving apparatus such as radar equipment are commonly referred to as radomes.
Nose radomes for transport jet aircraft are normally of sandwich construction. Most of these radomes incorporate a honeycomb core which is susceptible to impact damage and moisture ingestion. Moisture can enter the honeycomb through the damaged area or through pinholes created by electrostatic discharges or through the inherently porous facings associated with this construction. Water building up in the honeycomb cells will freeze and expand causing the damage to migrate. A layer of adhesive film is required for the honeycomb core radomes which increases cost of labor and material, and there is an inability to squeeze excess resin from the inside facing and precuring outside facing increases cost.
In U.S. Pat. No. 2,755,216 is disclosed the fluted core process for making radomes which utilizes wrapped wax mandrels, the wax being melted and drained from the radome after partial cure. The open flutes thus created allow any moisture that enters the core to be easily drained. These radomes have the disadvantages that they are contaminated with wax, are difficult to repair and do not have isotropic electrical and structural properties. Further, transmission performance does not meet new airline guidelines, dielectric breakdown voltage is poor and the cost is high.
With respect to existing foam core radomes, large sections of the foam are heat formed to shape in a tool prior to installing them in the mold against the outside facing, thus requiring extra tooling. Air and excess resin cannot be bled effectively from the outer facing through or around the large preformed foam sections. Heat forming the foam can cause thickness variations that are unacceptable electrically. Further, such radomes are difficult to repair in that each repair section must be heat formed, resulting in increased cost.
There is thus a need for a low cost light weight radome that will solve the above problems associated with honeycomb core, wax fluted core, and existing foam core radomes.